A variety of devices and methods have been developed in an effort to control the temperature stability of an inductor in a diversity of applications. However, these efforts have not always provided a satisfactory solution to the problem of controlling the temperature stability of an inductor in a multiplicity of these applications. Specifically, there is a temperature stability problem of an inductor employed in a proximity probe utilized for machine monitoring as a result of, inter alia, the severe temperature predations of the environment.
To operate safely and efficiently, rotating and reciprocating machinery require the use of various transducers. One such transducer is an eddy current or proximity probe which may be utilized for, inter alia, monitoring machine vibration characteristics. In this environment the proximity probe must operate under very adverse physical conditions.
Typically, the proximity probe, in conjunction with associated electronics, outputs a signal correlative to a spacing between a target object (e.g., a rotating shaft of a machine or an outer ring of a rolling element bearing) and a sensing coil of the proximity probe. It is critical that the length or spacing between the target and the sensing coil of the proximity probe remains within the linear range of the proximity probe for providing accurate and reliable measurements of machine vibration characteristics. Thus, one distinguishing characteristic for providing accurate and reliable measurement relies on providing a proximity probe which under the predations of its operating environment remains in the linear range of operation.
The electronics associated with the proximity probe typically incorporates some type of oscillation circuit whose amplitude of oscillations is dependent on the conductance of the included sensing coil. When the circuit is oscillating, the sensing coil has an alternating current flowing therein which causes the sensing coil to radiate energy in the form of an alternating magnetic field. The target object absorbs some of the radiated energy from the sensing coil when it is placed within the alternating field emanating from the sensing coil. This absorption of energy is a result of the alternating field generating eddy currents in the object which circulate so as to oppose the alternating field which created them. The amount of energy absorbed by the target object is correlative to the spacing between the target object and the sensing coil. The closer the target is to the sensing coil, the more energy the target will absorb from the sensing coil as a result of the eddy current principle. Therefore, the amplitude of oscillations of the oscillation circuit will vary as a function of spacing between the sensing coil and the target. Thus, this type of proximity probe system is advantageously employed for measurements needed when monitoring certain characteristics of rotating and reciprocating machinery. In these types of environments the proximity probe system must provide accurate and reliable measurements over a wide range of circuit and environmental conditions.
Heretofore, the ability to provide accurate and reliable measurements over a wide range of circuit and environmental conditions has been dependent on, inter alia, the characteristics of the sensing coil including the material and diameter of the wire used to wind the coil, the operating or resonance frequency of the system and the remaining electronics which constitute the proximity probe system. The sensing coil and the remaining electronics usually have a wide range of tolerances, such as gain, bias voltage, bias current and temperature coefficients. Accordingly, each production unit has to be initially calibrated to incorporate those tolerances. Moreover, the sensing coil of the proximity probe usually contains sources of temperature drift error which are attempted to be compensated for in the final product, usually at the expense of additional circuitry.
A principal source of the temperature drift error in the sensing coil is due to a temperature dependent resistance of the coil. This temperature dependent resistance of the sensing coil effects a source of temperature drift error resulting in inaccurate proximity probe measurements as a consequence of the false appearance of a gap change between the target and sensing coil. Such inconsistencies in temperature stability of the proximity probe result in unpredictable and unreliable measurements even when the proximity probe is functioning in its linear range of operation.
For the foregoing reasons, there is a need for controlling the temperature stability of a sensing coil of a proximity probe to preclude temperature drift and the resultant false appearance of gap change which leads to inaccurate and unreliable measurements of machine operating characteristics. In addition, there is a need to solve the general problem of setting the temperature response of resistance of an inductor to a value close to zero and to adjust the temperature coefficient of resistance of an inductor to compensate for anomalous behavior.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
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